1. Field of the Invention
The present invention relates to a process and an apparatus for manufacturing tyres for vehicle wheels.
The present invention further relates to a method of building at least one carcass ply during manufacture of a tyre for vehicle wheels.
In more detail, the invention is particularly directed to the process and equipment that, during building of a green tyre, are used for the purpose of manufacturing carcass plies.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures integrated into the regions usually identified with the name of “beads”, and having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective mounting rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers, disposed in radially superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band is applied at a radially external position to the belt structure, the tread band too being made of elastomeric material like other semifinished products constituting the tyre.
Respective sidewalls of elastomeric material are also applied at an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the tubeless type an airtight coating layer, usually identified as “liner”, covers the inner surfaces of the tyre.
Subsequently to building of the green tyre obtained through assembly of respective components, a vulcanisation and moulding treatment is generally carried out, said treatment aiming at causing structural stabilisation of the tyre by cross-linking of the elastomeric compounds, as well as at impressing it with a desired tread pattern and with possible distinctive graphic signs at the tyre sidewalls.
The carcass structure and belt structure are generally made separately from each other in respective work stations to be mutually assembled at a second time.
In more detail, manufacture of the carcass structure first involves application of the carcass ply or plies onto a building drum. Subsequently the annular anchoring structures to the beads are fitted or formed on the opposite end flaps of the carcass ply or plies and are afterwards turned up around the annular structures themselves so as to encompass them in a sort of loop to form a so-called substantially cylindrical “carcass sleeve”.
In the most widespread production processes, the carcass plies are made starting from an article of manufacture in the form of a continuous strip, formed of cords of textile, or in some cases metallic, material, disposed parallel to each other in a matrix of elastomeric material. Then a segment of a length corresponding to the circumferential extension of the carcass ply to be obtained is cut from said continuous strip. The segment is wound up on the outer surface of a building drum and the opposite ends thereof are joined together to form a carcass ply.
At the same time, a so-called “outer sleeve” is made on a second drum or auxiliary drum, which sleeve comprises the belt layers applied in radially superposed relationship with respect to each other, and possibly the tread band applied at a radially external position to the belt layers. The outer sleeve is then picked up from the auxiliary drum to be coupled with the carcass sleeve. To this aim, the outer sleeve is coaxially disposed around the carcass sleeve and then the carcass ply or plies are shaped into a toroidal configuration by axially approaching the beads to each other and simultaneously admitting fluid under pressure into the carcass sleeve, so as to give rise to radial expansion of the carcass plies until causing adhesion of same against the inner surface of the outer sleeve.
Assembly of the carcass sleeve to the outer sleeve can be carried out on the same drum as used for manufacturing the carcass sleeve, in which case the process is referred to as a “unistage building process”.
Also known are building processes of the so-called “two-stage type” in which a so-called “first-stage drum” is used to make the carcass sleeve, while assembly between carcass structure and outer sleeve is carried out on a so-called “second-stage drum” or “shaping drum” onto which the carcass sleeve picked up from the first-stage drum and subsequently the outer sleeve picked up from the auxiliary drum are transferred.
To the aims of the present specification and the following claims, by “strip-like element” it is intended an elongated article of manufacture having a cross-section profile with a flattened conformation and comprising one or more cords of textile and/or metallic material, extending parallel to the longitudinal extension of the strip-like element itself and embedded into, or at least partly coated with, at least one layer of elastomeric material.
Document E0928680 in the name of the same Applicant, shows that the carcass plies are made of strip-like elements formed with rubberised cords, laid down in circumferential mutually approached relationship on the outer surface of a toroidal forming support substantially conforming in shape to the inner conformation of the tyre being manufactured. One or more belt layers are subsequently formed by means of respective strip-like elements laid down in circumferential mutually approached relationship on the carcass ply or plies carried by the toroidal forming support.
Document WO01/38077 in the name of the same Applicant, shows that a belt structure is made of thread segments each comprising parallel cords embedded into an elastomeric layer and sequentially laid in circumferential mutually approached relationship on a toroidal support. During laying of each segment, an angular rotation of the toroidal support is determined around a correction axis radial to the rotation axis of the toroidal support itself, located at a substantially barycentric position relative to the segment that is about to be laid.